Several large scale facilities have been built in Canada, France, and more recently South Korea, to extract tritium from heavy water moderator systems for nuclear reactors. Kalyanam and Sood, “Fusion Technology” 1988, pp 525-528, provide a comparison of the process characteristics of these types of systems. Similar although smaller light water tritium recovery systems have been designed for fusion applications (see H. Yoshida, et al, “Fusion Eng. and Design” 1998, pp 825-882; Busigin et al, “Fusion Technology”, 1995 pp 1312-1316; A. Busigin and S. K. Sood, “Fusion Technology” 1995 pp 544-549). All current large scale tritium recovery systems employ a front-end process to transfer tritium from water to elemental hydrogen, followed by a cryogenic distillation cascade to perform all or most of the hydrogen isotope separation.
Thermal diffusion columns have been used to separate hydrogen isotopes on a small scale since the 1950's as described by G. Vasaru et al, “The Thermal Diffusion Column”, VEB Deutscher der Wissenschaften, Berlin, 1968.The use of this technology has been limited because it is not scaleable to large throughputs.
All commercial large scale processes for water detritiation are based on transfer of tritium from water to elemental hydrogen by: (a) a catalytic exchange reaction such as HTO+H2→H2O+HT; (b) direct electrolysis of water, i.e., HTO→HT+½O2; or (c) water decomposition by a suitable reaction such as the water gas shift reaction: HTO+CO→HT+CO2. (See Kalyanam and Sood “Fusion Technology” 1988, pp 525-528; A. Busigin and P. Gierszewski, “Fusion Engineering and Design” 1998 pp 909-914; D. K. Murdoch et al, “Fusion Science and Technology” 2005, pp 3-10; K. L. Sessions, “Fusion Science and Technology” 2005, pp 91-96; J. Cristescu et al, “Fusion Science and Technology” 2005, pp 97-101; J. Cristescu et al, “Fusion Science and Technology” 2005, pp 343-348.)
The prior art large scale hydrogen isotope separation cryogenic distillation process has the following drawbacks:    1. Handling of liquid cryogens with associated hazards, such as high pressure potential upon warm-up and evaporation, thermal stresses due to very low temperature process conditions and the requirement for a vacuum insulated coldbox vessel to contain the cryogenic equipment;    2. The potential for blockage of process lines due to freezing of impurities;    3. Complex and costly process plant;    4. Complex operation and maintenance;    5. Non-modular process, making it difficult to upgrade and to keep equipment spares;    6. Requires batch operated dryers and a liquid nitrogen adsorber to purify feed to the cryogenic distillation cascade.
Water distillation has been used in the past primarily for heavy water production and upgrading, and not specifically for tritium recovery. Tritium is easier to separate than deuterium from light water by water distillation. The elementary separation factors in distillation arise from differences in vapor pressures of the isotopic water species. For example, at a temperature of 51° C., the elementary separation factor for HDO/H2O is 1.052, whereas for HTO/H2O it is 1.064.The separation factor for DTO/D2O is much smaller at 1.012, making tritium recovery from heavy water by water distillation difficult. (W. Alexander Van Hook, Journal of Physical Chemistry, Vol. 72, No. 4, pp 1234-1244, 1968.)
Due to presence of natural deuterium at approximately 150 ppm, water distillation enrichment of tritium in light water is easy only when the deuterium concentration is small, which corresponds to a maximum practical enrichment in light water of about 1000 times. This degree of tritium enrichment is sufficient in many practical applications to reduce the tritium enriched product flow to a magnitude compatible with one or more downstream thermal diffusion columns, after conversion of water to an elemental hydrogen stream.
Thermal diffusion has been used successfully for small scale tritium separation, even up to ≧99% tritium, but cannot be easily scaled for large throughput. This is because thermal diffusion columns must operate in the laminar flow regime, and scale-up would push column operation into the turbulent flow regime (R. Clark Jones and W. H. Furry, “Reviews of Modern Physics”, 1946, pp 151-224). The alternative of constructing many small thermal diffusion columns in parallel is unattractive when the throughput requirement is large. Thermal diffusion columns also have low thermodynamic efficiency, which while unimportant at small scale becomes problematic at large scale.